The following is related generally to optical or fiberoptic components used in optical communication networks and, more specifically, to an optical device that can select a signal from a fiberoptic network that is carrying multiple optical signals, and reshape the wavelength spectrum of the selected signal.
Tunable optical filters are extensively used in modern, reconfigurable fiberoptic networks for a variety of purposes, including the selection of an individual channel or signal, from a fiber that is carrying multiple optical signals. In modern intelligent or re-configurable Wavelength Division Multiplexing (WDM) optical networks, the wavelength of an input optical signal may be changed from time to time. For example, a tunable optical transmitter may be used to generate the input optical signal. Thus, a tunable optical filter is desirable, and may be required to respond to the incoming wavelength change.
Furthermore, the optical signal power for each of the multiple optical signals is modulated to carry the desired information. The higher the modulation rate, the wider the bandwidth of the optical signal or wavelength. Ideally, a tunable optical filter should provide low insertion loss for the selected channel or wavelength, as well as a flat passband characteristic. As new modulation schemes are developed and deployed, it may also be desirable to shape the passband of the tunable optical filter in other ways. The designed width of the passband depends on a number of system or network-level parameters, including spacing of adjacent channels, as well as the modulation scheme and baud rate of the signals. At the same time, the tunable optical filter should provide high attenuation or isolation for channels or wavelengths that are adjacent to the selected channel or wavelength. These objectives are often in conflict with each other.